Examples of conventionally known molds used for curing an unvulcanized tire include: a bisplit mold including two, superior and inferior, pieces separated at the tire equatorial plane; and a sectional mold divided, in the circumferential direction of the tire, into plural pieces that expand and contract with respect to the center of the mold.
The bisplit mold is advantageous in making its equipment simple and small-sized, but has the following drawbacks. Releasing a tire having an intricate tread pattern, which is now common, from the bisplit mold is accompanied by a large resistant force. In addition, opening the mold with the tire adhering to the inner surface of the mold may result in the improper production of tires. Moreover, the use of bisplit mold may result in such other problems as cracking.
In contrast, the sectional mold, which has plural tread-segment portions divided in the circumferential direction of the tire, can deal with an intricate tread pattern. Nevertheless, the sectional mold requires providing, separately, a complex sliding mechanism, thereby resulting in an increase in the cost for the mold.
Under these circumstances, proposals have been made for molds for tire curing having a combined structure of a bisplit mold and a sectional mold (see, for example, Patent Documents 1 and 2).
Each of the proposed molds for tire curing has a structure that makes the plural divided segments expand and contract with respect to the center of the mold along with the opening-and-closing motion of vertically bisplit, superior and inferior, split shells. The use of elastic force of springs for the opening-and-closing action of the segmented mold, however, results in a complex structure. In addition, at mold clamping, mold clamping forces do not act uniformly on the segments, thereby preventing the stable mold clamping. The unstable clamping action causes a problem in that the unvulcanized tire is pinched between the segments, resulting in a defective tire product.
Patent Document 1: Japanese patent No. 3608161
Patent Document 2: Japanese patent application Kokai publication No. 2000-127173